Fluid catalytic cracking (FCC) is a well known process for the conversion of relatively high boiling point hydrocarbons to lighter hydrocarbons. In many catalytic cracking reactors, often referred to as riser reactors or risers, e.g., vertical pipe reactors, a relatively long chain hydrocarbon feedstock, e.g., gas oil or atmospheric residue, reacts in contact with a catalyst to produce shorter chain products and spent catalyst (e.g., catalyst particles covered with coke). This can be referred to as cracking the feed. The feedstock and fluidized catalyst are introduced at a lower entrance to the vertical riser, and travel vertically upwards within the riser reacting at very high temperatures until reaching an upper exit. The riser is often internally lined to minimize heat loss and resist erosion and/or corrosion.
Reaction efficiency in the riser depends, among other factors, on good and uniform mixing between the feedstock and fluidized catalyst. It is desirable that the feedstock be uniformly dispersed in a stream of fluidized catalyst that is moving up the riser. In many risers, however, even if near uniform dispersion is achieved at the riser entrance, non-uniform mixing can occur as the materials travel upwards due, at least in part, to non-uniform cross sectional gas and catalyst velocities that result primarily from the hydrodynamic condition known as core-annular flow typical of riser flow. In this condition, the upward velocity of the feedstock is lower near the riser wall and higher near the center. In this hydrodynamic regime, more dense fluidized catalyst tends to concentrate near the wall in the slower moving feedstock and on average travels at significantly lower velocity than the gas. The ratio between the average velocities of gas and catalyst may be referred to as reactor slip ratio and can be quite high. For example, high slip ratios of greater than about 1.7 can lead to lower reaction efficiency and yield.
Some attempts have been made to improve mixing along the vertical flow path of the riser. For example, obstacles such as baffles or other contact devices have been proposed to create turbulence and cause more uniform mixing in the riser. Unfortunately, implementing baffles in risers, which are typically relatively tall, e.g., heights of 10 to 50 meters (m), and narrow, e.g., internal diameters of 1 to 3 m, is difficult in general and is particularly problematic in retrofit situations in which the riser must be cut for access and erosion must be controlled downstream of the baffles.
Accordingly, it is desirable to provide apparatuses and risers for reacting a feedstock in the presence of catalyst and methods for fabricating such risers with improved implementation of baffles in the risers to increase reaction efficiency and yield. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.